The background description provided herein is for the purpose of generally presenting the context of the present invention. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present invention.
It is known that vehicle emissions are a major contributor to air pollution. In order to identify vehicles that are releasing excessive polluting emissions, many countries mandate annual vehicle emission inspections. To this purpose various vehicle emission inspection systems have been developed. Generally, these systems can be very expensive, and their operation can require a vast amount of labor and skill. Additionally, emission inspection systems have traditionally been operated in testing stations where the emissions are measured when the test vehicle is idling or running under artificially loaded conditions. Although such measurements provide general baseline information regarding a vehicle's emissions and state of repair, it is not necessarily representative of “real world” driving conditions.
Recently, remote emission sensing systems have been developed for detecting emissions of vehicles as they are driving on the road. For example, U.S. Pat. Nos. 5,319,199 and 5,498,872 to Stedman et al. discloses a remote sensing system in which the light source 1110 and detector 1130 are oppositely located on both sides of the road 1101, respectively, as shown in FIG. 9(a). For such an arrangement, a beam of light 1115 generated from the source 1110 passes through an exhaust plume 1140 emitted from a vehicle 1105 driven on the road 1101, thereby carrying an absorption signal associated with components and concentrations of the exhaust plume 1140. The beam 1115 is collected by the detector 1130 for analyzing the components and concentrations of exhaust plume 1140. Alternatively, as shown in FIG. 9(b), the light source 1110 and detector 1130 are located on the same side of the road 1101. And two reflectors 1150 located on the opposite side of the road 1101 are used to reflect the beam 1115 generated from the source 1110 to the detector 1130 with two passes through the vehicle exhaust plume 1140, which increases the absorption signal. This system measures only part of the plume and has to ratio the CO2 measurements to all other pollutants to get relative values. It does not measure the amount left behind or absolute values. Furthermore, for such remote emission sensing systems, the source, detector and reflectors are set up on both sides of the road, and much care needs to be taken during their installation and maintenance. Additionally, such a system is difficult to operate with more than one lane of traffic particularly when more than one vehicle passes through the detector simultaneously.
Current vehicle remote-sensing systems only sense part of the exhaust plume. If the infrared beams are large enough or use multi-pass beams with respect to the size of the plume they will encompass the entire plume. Since the entire plume is being sensed, then one can calculate absolute amounts and get grams-per-mile directly.
Conventionally, a non-dispersive infrared system usually uses an infrared beam 2 to 3 inches in diameter. The beam is directed across the road and reflected back through a series of mirrors. The system therefore only senses a percentage of the gases in the entire cross-section of the plume. The system then uses ratios to carbon dioxide to calculate the combustion equation. The combustion equation then gives you tailpipe percentages. Therefore, in order to get grams per mile one must calculate the vehicle specific power (VSP) and know model and make of the vehicle.
Further, when a vehicle starts up, the emissions mitigation system on the vehicle usually takes a warm-up time to warm up to a minimum temperature. The warm-up time is generally a minute or so, but can be much longer. Until the emission mitigation system reaches the minimum temperature, the exhaust plume may have carbon monoxide (CO), nitric oxide (NO), hydrocarbons and other pollutant above expectable levels such that the vehicle is not able to pass a typical emission test. Thus, if a vehicle is tested with a remote sensing device when it is cold (i.e. before the vehicle warms up), the remote sensing device will give a false negative reading. Current remote sensing devices are unable to identify such false negative readings from the real negative readings without the help of infrared cameras. Infrared cameras are used to see the reflection of a hot engine off the road surface and are costly separate units. Accordingly, current remote sensing devices are required to measure one vehicle with negative readings for at least 3 times at different locations to justify marking the vehicle as a dirty vehicle, as the chance of the same vehicle being cold in different locations and occasions are remote.
Therefore, a heretofore unaddressed need exists in the art to address the aforementioned deficiencies and inadequacies.